The long term goal of this project is to understand the mechanisms that are responsible for triggering the onset of puberty in our own species. In man and other higher primates, the hypothalamic GnRH pulse generating system, which, in the adult, provides the principal drive to the pituitary-gonadal axis, is functional during infancy. During prepubertal development, however, activity of the neuroendocrine axis governing primate gonadal function is arrested and held in a protracted state of quiescence by non-gonadal restraint of the hypothalamic GnRH pulse generator. Puberty in primates is thus triggered by a reawakening of GnRH pulse generator activity. Such a pubertal control system appears unique to man, apes and monkeys. Although puberty represents a major landmark in human development that is associated with dramatic changes in behavior, cognitive function, outlook, and, in some cases, with the onset of affective disorders, little is known about the fundamental neurobiology underlying the onset of this developmental stage. This problem will be addressed in the present proposal using the agonadal male rhesus monkey, a representative higher primate, as an experimental paradigm. The following Specific Aims Will be addressed: Specific Aim 1 - To test the hypothesis that an increase in NPY tone in the mediobasal hypothalamus (MBH) is a critical component of the restraint that is imposed upon pulsatile GnRH release during prepubertal development; Specific Aim 2 - To determine the phenotype of the synaptic input to GnRH perikarya that is lost during the transition from the juvenile to the pubertal state; Specific Aim 3 - To determine whether structural remodeling of the GnRH network at the level of the median eminence, in addition to that at the cell body and dendrites, occurs in association with the onset of the pubertal reaugmentation of pulsatile GnRH release; Specific Aim 4 - To determine whether inhibition of structural remodeling within the GnRH neuronal network at the end of the prepubertal phase of development prevents the onset of puberty. RNAse protection assays and in situ hybridization will be used to track developmental changes in NPY gene expression. Protein levels will be determined by Western blotting. The action of NPY in the MBH will be blocked using NPY receptor antagonists or antibodies administered intracerebroventricularly. Synthesis of NPY will be blocked with antisense oligodeoxynucleotides. Structural remodeling in the hypothalamus will be studied using both the light and electron microscope. Standard pre-embedding and post-embedding immunocytochemical procedures will be applied to quantitate changes in synaptic input and glial ensheathment of GnRH perikarya, dendrites and axonal terminals. Attempts will be made to block plasticity in the GnRH network of the pubertal hypothalamus by injecting or overexpressing endoneuraminidase in this region of the brain.